This course will provide extensive laboratory exposure to the biology and manipulation of embryos from the frog Xenopus laevis. Xenopus is a vertebrate uniquely suited for studies of early development, since large numbers of embryos, from fertilization onward, can easily be obtained. Development is rapid, and the large size of the embryos facilitates their micromanipulation to allow analysis of the role of cell interactions ("inductions') in development, in ways that are not feasible in mammalian embryos, such as mice. The course is particularly suited for those who have a current training in molecular biology and knowledge of developmental biology, but have had no experience with Xenopus. Five main areas will be covered both in the laboratory and by expert lecturers. These are: (1) care and handling of adults and embryos (2) stage of embryonic development and autonomy (3) whole mount in situ hybridization (4) microinjection of eggs and oocytes (5) microinjection of blastula and gastrula stages, and induction assays